1. R. E. Nettleton,J. Low Temp. Phys. 22, 407 (1976);24, 275 (1976);26, 277 (1977).
2. I. Rudnick,J. Low Temp. Phys. 40, 287 (1980).
3. L. D. Landau and E. M. Lifshitz,Theory of Elasticity (Pergamon Press, New York, 1959), p. 11.
4. G. Baym and C. J. Pethick, inThe Physics of Liquid and Solid Helium, K. H. Bennemann and J. B. Ketterson, eds. (Wiley, New York, 1978), Part II, p. 1.
5. J. C. Wheatley,Rev. Mod. Phys. 47, 415 (1975).